Test circuit for flame detector system



Dec. 20, 1955 M. H. NORTON TEsT CIRCUIT FOR FLAME DETECTOR SYSTEM Original Filed June 16, 1953 MA HLoN NORTON um 94 ATTORNEYS United States aten-t .i

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2,728,069v Y TEST- cmCUrr non MAME DErEcron SYSTEM Mahlon H. Norton, Paterson, N. 5. assignor to Petcar Research Corporation, Belleville, N. I., a corporation 0f New Jersey Continuation of application Serial No. 362,084, June 16, 1953 application July 23, 19.53, Serial No.

This application is a continuation of my corpending application Serial No. 362,084, filed lune l5, 1953.

This invention relates tol llame-detection systems of the type in which a signal is produced' when two electrodes forming part of the system gre bridged by a flame.

Such a system is disclosed in my co-pending application tern including two or more electrodes which are bridged by a llame to produce the signal indication.

The llame-detecting system provided by the invention of my co-pending application comprises two spaced Wires which are led in parallel, closely spaced relation through the space which is to be monitored. A source of alternatin Voltaoe is connected to one wire, which is known .A

and referred to hereinafter as the transmitting wire, and develops between this wire and ground an alternating voltage from which one hanncm'c of the frequency produced by the source is attenuated, it being understood that in the invention disclosed in my :zo-pending application the harmonic which is attenuated is a full-numbered harmonic which is neither the zero harmonic nor the basic frequency itself. The second wire, which is known and referred to hereinafter as the receiving wire, is connected to receiving means which is tuned to receive only that harmonic of the frequency produced by the source which has been attenuated in the voltage developed between the transmitting wire and ground. In the absence of a llame bridging the two wires, the energy supplied to the transmitting wire causes a field to be established about the two wires which normally is not received by the receiving means connected to the receiving wire because of the selective tuning thereof. However, a flame bridging the two wires causes immediate generation of the missing harmonic frequency in the output circuit of the receiving wire, thus developing energy which may be utilized to energize indicating means.

In the operation of such a llame-detecting system as that described above, it is necessary to know, or be able to know, at all times 'whether the system is operative and by the present invention l have provided a simple and elfective system or device for association with such a flame detecting system, which is operative at any time to provide an indication whether the entire llame detecting system is operable in the intended and designed manner.

An embodiment of the invention is described in the following specification and illustrated in the accompanying drawing, which is partly a schematic diagram and partly a circuit diagram showing a llame detector system having associated with it a test circuit according to the present invention.

A schematic diagram of a llame detecting system constructed and operable in accordance with the invention of my co-pending application and including test means in accordance with the present invention, is disclosed in the drawings and comprises a transmitting electrode 2 and a receiving electrode 4 which, in the disclosed Patented Dec. 20, 1955 nacelle A Source, 0f alternating voltage 8 is Connected to the transmitting wire 2 through a null filter 10 which eliminates from the energy supplied to the wire 2 one harmonic of the frequency generated by the source, and an amplifier 12, thus causing an alternating voltage to be developed between the wire 2 and ground having all of the basic and harmonic frequencies produced by the Source 8 but with a negligible quantify @t the harmonie frequency attenuated by filter lil. The receiving wire 4 is connected through amplifier 2Q, amplitude selector 22, counting rate circuit 24 and relay control tube4 2 6 to a relay .23 which is operable, when energized, to close the circuit through an indicating device such as lamp $0,

The rest Circuit provided bv this invention comprises a normally open two-contact switch eil, one terminal of WIV-ich 11S, @entered threueh resistors 4Z. 44 te the Output of the null filter 1i? and the input of amplifier 12, and the other terminal of which is connected to one terminal of a potentiometer 46, the other terminal of which is grounded at 43. The Contact arm of the potentiometer is connected to one element of a diode device 50 which may be a vacuum tube, semi-conductor device, transistor or the like, the other element of which is grounded at 48.

In the normal operation of the llame detector system, an harmonic of the basic frequency of the source 8 is attenuated from the energy supplied to the amplier 12 and transmitting wire 2. lf the test switch 4@ is closed this energy, without the attenuated harmonic, will be supplied through the potentiometer 45 to the diode device 50 and rectication will talte place and will be partial or complete, depending on the setting of the contact arm of the potentiometer. This rectification will supply to the transmitting wire a controllable amount of the previously attenuated harmonic of the basic frequency and as the output circuitry of the receiving wire is tuned to receive only energy having the attenuated harmonic frequency, and as there is a measurable capacitance between the transmitting and receiving wires, the output circuitry of the receiving wire will be energized and the indicator 30 will be operated in the usual and described manner, thus providing an indication that the system is operative in its intended manner.

While l have described and illustrated one form which my invention may take, it will be apparent to those skilled in the art to which it relates that other embodiments, as well as modifications of that disclosed, may be made and practised without departing in any way from the spirit or scope of the invention, for the limits of which reference must be had to the appended claims.

What is claimed is:

1. An electrical llame detecting system comprising electrode means positioned within a space to be monitored for llame and insulated from ground, means for developing in said electrode means an alternating voltage of a known fundamental frequency containing known measurable harmonics from which at least one harmonic of the fundamental frequency has been attenuated to negligible value, which attenuated harmonic is neither the zero nor iirst harmonic of the fundamental frequency, receiving means coupled to said electrode means which is responsive only to the attenuated harmonic of the fundamental frequency, means for indicating reception of said attenuated harmonic, means connected between said electrode means and ground for supplying electrical energy at the frequency of the attenuated harmonic to said electrode means, and means for disconnecting said last-named means from the electrode means.

2. An electrical ame detecting system comprising two spaced electrodes positioned within a space to be monitored and adapted to be bridged by a flame, meansfor developing between one electrode and ground an alternating voltage of a known fundamental frequency containing known measurable harmonics from which at least one harmonic of the fundamental frequency has been attenuated to negligible value which is neither the zero nor first harmonic of the fundamental frequency, receiving means connected between the second electrode and ground which is responsive only to the attenuated harmonic of the fundamental frequency, means for indicating reception of said attenuated harmonic or harmonics, means connected between the first named electrode and ground for supplying electrical energy at the frequency of the attenuated harmonic to the first electrode, and means for disconnecting said last-named means from the first electrode.

3. An electrical ame detecting system comprising two spaced electrodes positioned within a space to be monitored and adapted to be bridged by a flame, means for developing between one electrode and ground an alternating voltage of a known fundamental frequency con- 4 taining known measurable harmonics from which at least one harmonic of the fundamental frequency has been attenuated to negligible value, which is neither the zero nor iirst harmonic of the fundamental frequency, receiving means connected between the second electrode and ground which is responsive only to the attenuated harmonic or harmonics of the fundamental frequency, means for indicating reception of said attenuated harmonic or harmonics, rectifying means having one element thereof grounded, a potentiometer connected between ground and said rst electrode and having its contact arm connected to the second element of said rectifying means, anda normally open switch in circuit between the potentiometer and the first electrode for connecting the same when operated to closed position to cause energy at the frequency of the attenuated harmonlc to be supplied to said electrode.

2,580,539 Goodwin Jan. 1, 1952 

